1. Field of the Invention
This invention relates to a gas combustion type driving tool, more particularly to a fastener feeding device for a gas combustion type driving tool.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a gas combustion type driving tool 1 disclosed in U.S. Pat. No. 7,556,182 B2 is shown to include a striking piston 181 driven by a combustion gas to move within a striking cylinder 11 of a tool body 12 so as to move a driver 182 out of a nose part 121 for driving a fastener 2 into a targeted object (A). A fastener feeding device 19 includes a feed cylinder 191 and a feed piston 192 urged by a spring 193 to move in a feeding direction within the feed cylinder 191. The feed cylinder 191 is in fluid communication with a combustion chamber 10 through a gas conduit 15, and a delay piston/cylinder device 16 is disposed in the gas conduit 15. A first check valve 151 and a second check valve 152 are disposed downwardly of the delay piston/cylinder device 16, and a switch valve 17 is disposed between the second check valve 152 and the feed cylinder 191. In a nail driving operation, when the nose part 121 is pressed against the targeted object (A) to move a contact arm 14 upward, the combustion gas is injected into the combustion chamber 10 and is mixed with air. Once a trigger 13 is pulled, the mixed gas is ignited, burned, and expanded explosively. The pressure of the combustion gas acts onto the striking piston 181 to drive the nail 2. Meanwhile, the pressure of the combustion gas also acts onto the delay piston/cylinder device 16, and the air which is introduced therein from the atmosphere through the first check valve 151 is compressed. Consequently, the compressed air is admitted into the feed cylinder 191 through the second check valve 152 so as to rise up to sufficiently move the feed piston 192 against the spring 193, thereby performing a fastener feeding operation. Thus, the supply of the pressure of the combustion gas from the combustion chamber 10 to the feed cylinder 191 can delay the fastener feeding operation.
However, since the carbon content of the combustion gas is quite high, carbon may accumulate in the conduit 15 to adversely affect the fastener feeding operation.
Another fastener driving tool as disclosed in U.S. Publication No. 20080314953 is provided with an electromechanical retention device that is operationally associated with a fastener feeding mechanism for causing a difference in the operation timing between a striking process and a fastener feeding process. However, the provision of the electromechanical retention device renders the structure of the fastener driving tool quite complicated.